Finally I managed to enter in SSH...I found that /etc/upstart was pretty empty so I added all missing files from my backup, I rebooted in main mode but no luck....I'm still under the tree....
What to try next?

WHICH /etc/upstart? The one you see when you boot diags is on the diags partition. It SHOULD be mostly empty.

You should do this instead, to see the "real" /etc/upstart:mount /dev/mmcblk0p1 /mnt/mmc
cd /mnt/mmc/etc/upstart
ls -al

I have limited info about this but i think its better to use mmcblk0p2 of the same version with mmcblk0p1. But I don't know about requirements and specific installation of kernels.

But just remembered that there is a good page about this whole process: tinyurl.com/touchunbrick

It is important that a partition and its kernel be the same version, but main and diags did not have to match in the past. Now that 5.1.0 changes both main and diags, they may both have to be 5.1.0 to prevent problems when doing an OTA update.

That Russian web page does bring all the stuff to one place, including my screenshots, my custom u-boots, my custom diags partititon (I put the "mario" password into the diags shadow file), and stuff from my other threads. I put that jagged line in my MfgTool screenshot to make it fit the MobileRead column width without shrinking it to make the text too small. He did provide a link back to my one of my threads after I sent him a message that requested that he give credit to the sources of his information and an optional link. He added the link, but "geekmaster" is not found on his web page. That is why I added the "CC BY-SA" license to all my recent posts (which requires user attribution when you copy stuff). Copying stuff without giving credit is just simple plagiarism even if you do add some of your own stuff to it. It is good to have a Russian translation of my stuff, but what I see here (and other threads) is a link to an ENGLISH translation of a Russian version of my original English stuff. He does have it all in one place, but that does not give him right to publish without giving credit to those who CREATED that content.

It is important that a partition and its kernel be the same version, but main and diags did not have to match in the past. Now that 5.1.0 changes both main and diags, they may both have to be 5.1.0 to prevent problems when doing an OTA update

We do not provide direct clickable links, to stay within mobileread forum guidelines. The first post of the "simple debricking" thread has a link to a pastebin page with URLs. One of those URLs is for the gitbrew forensic page listed above.

@silver18: Was it the "forensic images" link description that made you NOT click the link to find the image you needed?

I'm in the middle of getting somewhere...
I managed to mount mmcblk0p1, I fixed the dbus.conf file, now I need to reboot but selecting "exit diagnostic" tells me that user partition isn't ready.
Do I need to unmount it? How?

It is good to have a Russian translation of my stuff, but what I see here (and other threads) is a link to an ENGLISH translation of a Russian version of my original English stuff. He does have it all in one place, but that does not give him right to publish without giving credit to those who CREATED that content.

You are quite right. Well, after silver18 will prepare a good and proper tutorial, we will not need it anymore. Sorry, at least I could mention about this stuff but I thought that it's obvious that the actual source is your threads on this forum hence did not bother to mention about it.

I'm in the middle of getting somewhere...
I managed to mount mmcblk0p1, I fixed the dbus.conf file, now I need to reboot but selecting "exit diagnostic" tells me that user partition isn't ready.
Do I need to unmount it? How?

Sorry to be so rude, I'll answer everything later!

Gotcha! The un-mount command is spelled with only one 'n' :
umount /dev/<whatever_you_mounted>

I'm in the middle of getting somewhere...
I managed to mount mmcblk0p1, I fixed the dbus.conf file, now I need to reboot but selecting "exit diagnostic" tells me that user partition isn't ready.
Do I need to unmount it? How?

Sorry to be so rude, I'll answer everything later!

Exiting from the diags menu that way requires a folder and file to exist that may be missing (see the wiki). They are created by the first item in the main diags menu. It is simpler to exit using an SSH prompt:

I did "fsck -nf /dev/mmcblk0p1" and it told me about the missing "/lost+found" folder. That is normal for a kindle. The startup scripts delete that folder after creating ext3 partitions.

On my linux host PC, fsck also allows checking partition image files.

Perhaps you have a damaged partition image file. In another thread, use ppoo recently had the same problem as you, and it appears that he solved it by downloading and flashing a fresh copy of the partition file.

I did "fsck -nf /dev/mmcblk0p1" and it told me about the missing "/lost+found" folder. That is normal for a kindle. The startup scripts delete that folder after creating ext3 partitions.

On my linux host PC, fsck also allows checking partition image files.

Perhaps you have a damaged partition image file. In another thread, use ppoo recently had the same problem as you, and it appears that he solved it by downloading and flashing a fresh copy of the partition file.

Only devices that contain an "unmounted" filesystem.
The losetup command (if present) should turn a file into a device (it can also turn a device+offset into a device).
On the "full" implementation of the "mount" command, the -o loop option calls "losetup" for the user. The stripped down version lets the user do the calling.